The present invention relates to a class of novel precursors for chemical vapor deposition of silicon nitride, silicon oxide, and silicon oxynitride. In particular, the present invention relates the synthesis of hydrazinosilanes and their applications as low temperature CVD precursors for silicon dielectric films in the fabrication of integrated circuit devices. These precursors may also be used for atomic layer deposition, plasma enhanced chemical vapor deposition, and atmospheric pressure chemical vapor deposition.
Silicon-containing dielectric depositions play an important role in the fabrication of integrated circuits. Silicon nitride can be used on semiconductor devices as diffusion barriers, gate insulators, for trench isolation, and capacitor dielectrics. Low temperature CVD process is the method widely accepted by semiconductor industry for silicon nitride film fabrication.
In the fabrication of semiconductor devices, a thin passive layer of a chemically inert dielectric material such as, silicon nitride (Si3N4) is essential. Thin layers of silicon nitride function as diffusion masks, oxidation barriers, intermetallic dielectric material with high dielectric breakdown voltages and passivation layers. The nitride films are used as sidewall spacers in MOS devices and, with oxides, and oxynitrides, gate dielectrics for Groups IV and II-V transistors. Many other applications of silicon-containing dielectric in the fabrication of semiconductor devices are reported elsewhere, see Semiconductor and Process technology handbook, edited by Gary E. McGuire, Noyes Publication, New Jersey, (1988), pp 289–301; and Silicon Processing for the VLSI ERA, Wolf, Stanley, and Talbert, Richard N., Lattice Press, Sunset Beach, Calif. (1990), pp 20–22, 327–330.
The present semiconductor industry standard silicon nitride growth method is by low pressure chemical vapor deposition in a hot wall reactor at >750° C. using dichlorosilane and ammonia.
Deposition of silicon nitride over large numbers of silicon wafers has been accomplished using many precursors. The low pressure chemical vapor deposition (LPCVD) using dichlorosilane and ammonia requires deposition temperatures greater than 750° C. to obtain reasonable growth rates and uniformities. Higher deposition temperatures are typically employed to get the best film properties. There are several drawbacks in these processes and some of these are as follows:                i) Silane and dichlorosilane are pyrophoric, toxic compressed gases; and        ii) Films from dichlorosilane have contaminants, such as chlorine and ammonium chloride, which are formed as byproducts.        
Several classes of chemicals are used as precursors for silicon nitride film deposition. Among them are silanes, chlorosilanes, polysilazanes, aminosilanes, and azidosilanes.
Japanese Patent 6-132284 describes deposition of silicon nitride using organosilanes with a general formula (R1R2N)n SiH4−n (where R1 and R2 range from H—, CH3—, C2H5—, C3H7—, iso-C4H9—) by a plasma enhanced chemical vapor deposition and thermal chemical vapor deposition in the presence of ammonia or nitrogen. The precursors described here are tertiary amines and do not contain NH bonding as in the case of the present invention. The deposition experiments were carried out in a single wafer reactor at 400° C. at high pressures of 80–100 Torr. The Si:N ratios in these films were 0.9 (Si:N ratios in Si3N4 films is 0.75) with hydrogen content in the deposited films.
Sorita et al., J. Electro.Chem. Soc., Vol 141, No12, (1994), pp 3505–3511, describe deposition of silicon nitride using dichlorosilane and ammonia using a LPCVD process. The major products in this process are aminochlorosilane, silicon nitride and ammonium chloride. Formation of ammonium chloride is a major drawback of using Si—Cl containing precursors. The formation of ammonium chloride leads to particle formation and deposition of ammonium chloride at the backend of the tube and in the plumbing lines and the pumping system. Processes which contain chlorine in the precursors result in NH4Cl formation. These processes require frequent cleaning and result in large down time of the reactors.
B. A. Scott, J. M. Martnez-Duart, D. B. Beach, T. N. Nguyen, R. D. Estes and R. G. Schad., Chemtronics, 1989, Vol 4, pp 230–234., report deposition of silicon nitride using silane and ammonia by LPCVD in the temperature region of 250–400° C. Silane is a pyrophoric gas and is difficult to control for the deposition of clean silicon nitride due to partial gas phase reaction.
J. M. Grow, R. A. Levy, X. Fan and M. Bhaskaran, Materials Letters, 23, (1995), pp 187–193, describe deposition of silicon nitride using ditertiarybutylsilane and ammonia by LPCVD process in the temperature range of 600–700° C. The deposited silicon nitride films were contaminated with carbon impurities (10 atomic %). This is mainly due to the presence of direct Si—C bonds in the precursor.
W-C. Yeh, R. Ishihara, S. Moishita, and M. Matsumura, Japan. J. Appl. Phys., 35, (1996) pp 1509–1512, describe a low temperature deposition of a silicon-nitrogen film using hexachlorodisilane and hydrazine near 350° C. The films are unstable in air and slowly convert to an silicon-oxygen film.
A. K. Hochberg and D. L. O'Meara, Mat. Res. Soc. Symp. Proc,. Vol. 204, (1991), pp 509–514, report deposition of silicon nitride and silicon oxynitride by using diethylsilane with ammonia and nitric oxide by LPCVD. The deposition was carried out in the temperature range of 650° C. to 700° C. The deposition is limited to deposition at 650° C. and the deposition rate drops to below 4 Å/min at lower temperatures. In the LPCVD process, precursors which contain direct Si—C carbon bonds result in carbon contamination in the films. Carbon free deposition requires greater than 5:1 NH3 to precursor ratios. At lower ammonia concentrations, the films were found to contain carbon. Diethylsilane and ammonia processes typically require covered boats or temperature ramping to improve uniformities across the wafers.
U.S. Pat. No. 5,234,869 and R. G. Gordon and D. M. Hoffman, Chem. Mater., Vol. 2, (1990), pp 482–484 disclose other attempts to reduce the amount of carbon involved aminosilanes, such as tetrakis(dimethylamino)silane. The temperature of deposition is in the range of 300–1000° C. with pressures in the range of 1 mTorr-10 Torr. The presence of direct Si—N bonds and the absence of Si—C bonds were expected to give lower carbon concentrations in the films. However, there are three main disadvantages with precursors of this class.                1) They contain N-methyl groups, the methyl groups tend to migrate to the silicon surface readily and contaminate the films with carbon during a CVD process. In order to reduce the amount of carbon, the process involves high temperatures (>700) and high ammonia ratios (>10:1). With increased ammonia ratios the deposition rates dramatically reduce due to reactant depletion.        2) They do not contain NH bonding and they do not involve secondary silanes.        3) At lower temperatures the deposition rates and uniformities are very poor (>5%).        
U.S. Pat. No. 5,874,368 describes our previous work to reduce the nitride deposition temperature to below 550° C. using bis(tertarybutylamino)silane (“BTBAS”). This temperature is still too high for depositions on circuits with metallization and on many Group III-V and II-VI devices. In addition, the precursor has a high activation energy that makes the process very temperature sensitive.
The trend of miniaturization of semiconductor devices and low thermal budget requires lower process temperature and higher deposition rate. A process involve a typical precursor such as BTBAS requires process temperature at least 550° C. Chlorosilanes need temperature even higher.
Ammonia plays an important role in silicon nitride CVD as nitrogen source. Hydrazine and its derivatives have been used as reagent for silicon surface nitradation[6–10], and also been used to replace ammonia as nitrogen source to react with chlorosilanes[11–13].
Although hydrazinosilanes were first synthesized several decades ago[1–2], very little research works have been conducted in this field. Some researchers have been interested in the chemistry of cyclic hydrazinosilanes in recent years[3–5]. However, in general those cyclic hydrazinosilanes have high molecular weight and, therefore, high boiling point. The high boiling point, or low vapor pressure, would be less preferred for CVD applications. No silicon-containing dielectric application of hydrazinosilanes has been published, especially for the open chain hydrazinosilanes.
The unusual reactivity of hydrazinosilanes is generally attributed to the weakness of the N—N bond linkage and hence the case with which it is homolytically cleaved.
The bond energy of N—N bond in 1,1-dimethylhydrazine (246.9 kJ/mol) is much less than that of Si—H bond in Me3SiH (377.8 kJ/mol), Si—C bond in s-Bu-SiMe3 (414 kJ/mol), and N—C bond in t-butylamine (362 kJ/mol)[15].
The present invention has overcome the problems of the prior art with the use of a group of precursors unique to the formation of silicon-containing dielectric films that are grown at low thermal conditions (to below 400° C.), have reduced carbon contamination, and have low hydrogen contamination. In addition, the precursors have very low activation energies that make processing less temperature sensitive, avoiding chlorine contamination and operate over a wide range of pressures (10−5 Torr–760 Torr) in a manufacturing batch furnace or a single wafer reactor as will be described in greater detail below.